Exposed imaging plates contain a latent X-ray image, in the form of locally excited metastable excited states of colour centres, which is obtained by the imaging plate being placed behind an object in X-ray light generated by an X-ray source.
This latent image is read out by the imaging plate being scanned, point by point, with a readout beam of small diameter. The wavelength of the readout light is chosen in such a way that it excites a metastable excited centre into a higher electron state which rapidly decays, accompanied by fluorescence.
The fluorescent light emitted in such a way is measured with a detection device which, for example, may contain a photomultiplier by way of light-sensitive element. From the electrical output signal of the detection means and from electrical signals that reproduce the instantaneous position of the readout beam, an image of the transmission of the object, expressed by electrical signals, can then be obtained.
An advantage of the imaging plates in comparison with conventional X-ray films is the fact that the imaging plates can often be used again. Since in the course of the readout procedure some of the excited electron states of the centres remain behind by reason of the only brief local exposure by the readout beam, it is necessary to erase the imaging plate reliably before a new recording by irradiating it intensely and for a relatively long time with erasing light. If this is not done, a shadow of the preceding X-ray image may appear on the next X-ray image.
The erasing devices that have been used hitherto for imaging plates are separate instruments, into which the imaging plates are passed when they have left the readout device. With regard to the high costs of the imaging plates and the large number of radiographs that are taken in hospitals and similar institutions, it is advantageous if an imaging plate is available again as quickly as possible after the latent image has been read out.
The present invention is directed to addressing these and other matters.